Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$91.47	6.609%	$97.5153	$97.52	$97.50	$97.50
Purchase #2	$144.37	12.225%	$162.0192	$162.02	$162.00	$162.00
Purchase #3	$109.62	6.307%	$116.5337	$116.53	$116.55	$116.50
Purchase #4	$91.81	6.167%	$97.4719	$97.47	$97.45	$97.50
Purchase #5	$94.38	6.212%	$100.2429	$100.24	$100.25	$100.20
Purchase #6	$246.60	12.544%	$277.5335	$277.53	$277.55	$277.50
Purchase #7	$226.74	13.159%	$256.5767	$256.58	$256.60	$256.60
7 purchase totals =	$1,004.99		$1,107.8932	$1,107.89	$1,107.90	$1,107.80